Previously, a known electronic apparatus controls a drive operation of an electric motor of, for example, an electric power steering system through a plurality of drive circuits that form a plurality of systems, respectively. In a case where one of the drive circuits fails, the electronic control apparatus stops the failed drive circuit and executes the control operation for driving the electric motor through the remaining normal one of the drive circuits.
For example, an electronic apparatus of JP2008-230540A (corresponding to US2008/0230302A1) has a thermistor, which functions as a temperature sensor. This electronic apparatus limits the amount of electric current supplied to electronic components in such a manner that the temperature of the electronic components is kept within a temperature range, in which the electronic components are operable, while the temperature sensed with the thermistor is used as a reference temperature. In this way, the electronic apparatus limits thermal destruction of the electronic components.
However, in the electronic apparatus of JP2008-230540A (corresponding to US2008/0230302A1), a location of the thermistor on the circuit board is not defined. Therefore, in the case of the electronic apparatus having the multiple drive circuits that form the multiple systems, respectively, the following disadvantages may possibly occur depending on the location of the thermistor.
For instance, it is assumed that the thermistor is placed at a location where one of the drive circuits, which form the multiple systems, respectively, has a large influence on the thermistor. In such a case, when the one of the drive circuits fails, the temperature, which is sensed with the thermistor, is decreased. In such a case, the amount of electric current, which can be supplied to the remaining normal one(s) of the drive circuits, is set based on the reference temperature that is lower than the actual temperature of the electronic components of the normal drive circuit(s). Therefore, when the excess amount of electric current, which may cause an increase in the temperature of the electronic components beyond the operable temperature of the electronic components, is supplied to the electronic components of the normal drive circuit, the normal drive circuit may possibly fail due to the excess amount of heat generated from the electronic components of the normal drive circuit.
In order to address the above disadvantage, it is conceivable to provide a plurality of thermistors to the drive circuits, respectively, which form the multiple systems. However, in such a case, a size of the electronic apparatus is disadvantageously increased, and the costs of the electronic apparatus are disadvantageously increased.